Even though the automotive industry has over the years, if for no other reason than seeking competitive advantages, continually exerted efforts to increase the fuel economy of automotive engines, the gains continually realized thereby have been deemed by various levels of government as being insufficient. Further, such levels of government have also arbitrarily imposed regulations specifying the maximum permissible amounts of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NO.sub.x) which may be emitted by the engine exhaust gases into the atmosphere.
Unfortunately, generally, the available technology employable in attempting to attain increase in engine fuel economy is contrary to that technology employable in attempting to meet the govermentally imposed standards on exhaust emissions.
For example, the prior art in trying to meet the standards for NO.sub.x emissions has employed a system of exhaust recirculation whereby at least a portion of the exhaust gas in reintroduced into the cylinder combustion chamber to thereby lower the combustion temperature therein and consequently reduce the formation of NO.sub.x.
The prior art has also proposed the use of engine crankcase recirculation means whereby the vapors which might other-wise become vented to the atmosphere are introduced into the engine combustion chambers for further burning.
The prior art has also proposed the use of fuel metering means which are effective for metering a relatively overly rich (in terms of fuel) fuel-air mixture to the engine combustion chamber means as to thereby reduce the creation of NO.sub.x within the combustion chamber. The use of such overly rich fuel-air mixtures results in a substantial increase in CO and HC in the engine exhaust which, in turn, requires the supplying of additional oxygen, as by an associated air pump, to such engine exhaust in order to complete the oxidation of the CO and HC prior to its delivery into the atmosphere.
The prior art has also heretofore proposed employing the retarding of the engine ignition timing as a further means for reducing the creation of NO.sub.x. Also, lower engine compression ratios have been employed in order to lower the resulting combustion temperature within the engine combustion chamber and therby reduce the creation of NO.sub.x. In this connection the prior art has employed what is generally known as a dual bed catalyst. That is, a chemically reducing first catalyst is situated in the stream of exhaust gases at a location generally further away from the engine and downstream of the first catalyst. The relatively high concentrations of CO resulting from the overly rich fuel-air mixture are used as the reducing agent for NO.sub.x in the first catalyst while extra air supplied (as by an associated pump) to the stream of exhaust gases, at a location generally between the two catalysts, serves as the oxidizing agent in the second catalyst. Such systems have been found to have various objections in that, for example, they are comparatively very costly requiring additional conduitry, air pump means and an extra catalyst bed. Further, in such systems, there is a tendency to form ammonia which, in turn, may or may not be reconverted to NO.sub.x in the oxidizing catalyst bed.
The prior art has also proposed the use of fuel metering injection means for eliminating the usually employed carbureting apparatus and, under superatmospheric pressure, injecting the fuel through individual nozzles directly into the respective cylinders of a piston type internal combustion engine. Such fuel injection systems, besides being costly, have not proven to be generally successful in that the system is required to provide metered fuel flow over a very wide range of metered fuel flows. Generally, those prior art injection systems which are very accurate at one end of the required range of metered fuel flows, are relatively inaccurate at the opposite end of that same range of metered fuel flows. Also, those prior art injection systems which are made to be accurate in the mid-portion of the required range of metered fuel flows are usually relatively inaccurate at both ends of that same range. The use of feedback means for altering the metering characteristics of such prior art fuel injection systems has not solved the problem of inaccurate metering because the problem usually is intertwined within such factors as: effective aperture area of the injector nozzle; comparative movement required by the associated nozzle pintle or valving member; inertia of the nozzle valving member; and nozzle "cracking" pressure (that being the pressure at which the nozzle opens). As should be apparent, the smaller the rate of metered fuel flow desired, the greater becomes the influence of such factors thereon.
It is now anticipated that the said various levels of government will be establishing even more stringent exhaust emission limits.
The prior art, in view of such anticipated requirements, with respect to NO.sub.x, has suggested the employment of a "three-way" catalyst, in a single bed, within the stream of exhaust gases as a means of attaining such anticipated exhaust emission limits. Generally, a "three-way" catalyst is a single catalyst, or catalyst mixture, which catalyzes the oxidation of hydrocarbons and carbon monoxide and also the reduction of oxides of nitrogen. It has been discovered that a difficulty with such a "three-way" catalyst system is that if the fuel metering is too rich (in terms of fuel) the NO.sub.x will be reduced effectively but the oxidation of CO will be incomplete; if the fuel metering is too lean, the CO will be effectively oxidized but the reduction of NO.sub.x will be incomplete. Obviously, in order to make such a "three-way" catalyst system operative, it is necessary to have very accurate control over the fuel metering function of the associated fuel metering means feeding the engine. As hereinbefore described, the prior art has suggested the use of fuel injection means, employing respective nozzles for each engine combustion chamber, with associated feedback means (responsive to selected indicia of engine operating conditions and parameters) intended to continuously alter or modify the metering characteristics of the fuel injection means. However, as also hereinbefore indicated, such fuel injection systems have not proven to be successful.
It has also heretofore been proposed to employ fuel metering means, of a carbureting type, with feedback means responsive to the presence of selected constituents comprising the engine exhaust gases. Such feedback means were employed to modify the action of a main metering rod of a main fuel metering system of a carburetor. However, tests and experience have indicated that such a prior art carburetor and such a related feedback means can never provide the degree of accuracy required in the metering of fuel to an associated engine as to assure meeting, for example, the said anticipated exhaust emission standards.
It is well known that in starting an engine, under cold starting conditions, it is difficult to achieve a sufficient fuel-vapor/air ratio to start the engine due to the low vapor pressures of gasoline to low temperatures. In conventional prior art carburetors, this problem is generally overcome by the use of a choke valve or plate as in the inlet of the induction passage with such choke valve serving to, at cold starting conditions, restrict the inlet of the induction passage thereby decreasing the pressure downstream thereof and causing a much greater quantity of fuel flow to be fed to the engine; such greater quantity of fuel is usually a rate of fuel flow far greater than the rate of fuel flow provided to the engine during normal engine temperature operating conditions. Therefore, even with a relatively small percentage of vaporization of such fuel, the increased amount of fuel provides a fuel-vapor/air ration sufficient to start and run the cold engine.
The prior art fuel injection systems experience the same problem even though, generally, injection systems exhibit improved fuel atomization characteristics as compared to carburetors. The prior art has attempted to solve this problem generally in the same way that carburetors have solved the problem. That is, since at cold conditions a lesser percentage of the fuel is vaporized, to overcome such vapor deficiency, more fuel is supplied as to achieve the total fuel vapor required. Accordingly, in such injection systems, the prior art has provided means responsive to engine and/or ambient temperature effective for causing increased metered rates of fuel flow during a preselected range of relatively low temperatures.
The prior art method, of thusly metering increasing rates of fuel flow during cold engine starting and operation, has several disadvatages. For example, and obviously, the practice of such prior art method requires far larger quantitites of fuel to be supplied to the engine than would otherwise be necessary (if the engine were at normal temperatures). Since, during such cold start conditions, only the lightest most volatile portion of the fuel vaporizes, the heavier or less volatile portions of the fuel either pass through the engine unburned or puddle as in the engine intake manifold. The fuel that thusly passes through the engine unburned exhibits itself as unburned hydrocarbons in the exhaust gases while the fuel that puddles eventually vaporizes, as the intake manifold warms-up with continued engine operation, making the fuel-air ratio then supplied to the engine overly rich (in terms of fuel) to the detriment of carbon monoxide emission production.
Another disadvantage of the prior art, namely, depending on the lightest or most volatile portion of the fuel to vaporize, is that such dependence, in turn, makes cold starting of an engine a direct function of fuel quality and a special blended winter fuel is required wherein a large fraction thereof is composed of highly volatile components in order to achieve good cold engine starting characteristics.
Accordingly, the invention as herein disclosed is primarily directed to the solution of the problems of the aforedescribed prior art and other related and attendant problems.